1. Field of the Invention
The present invention generally relates to insulating elements, and more particularly to an electrically insulating element which is mounted on a circuit board and spatially isolates a high voltage element and a low voltage element on the circuit board. Further, the present invention is concerned with a circuit board using such an electrically insulating element.
Recently, it has been required that in the field of development and production of electric products, the structures of these electric products satisfy safety requirements according to various standards such as IEC (International Electrotechemical Commission), UL (Underwriters Laboratory Inc.), and CSA (Canadian Standards Association). One of the safety requirements is an isolation space distance, which depends on the potential difference between parts.
2. Description of the Prior Art
FIG. 1A is a diagram showing an arrangement of parts mounted on a printed circuit board. Conventionally, an electric product such as a CRT (Cathode Ray Tube) has a printed circuit board on which high-voltage parts and low-voltage parts are mounted. Referring to FIG. 1A, a high-voltage component 12 and a low-voltage component 13 are mounted on a mounting surface of a printed circuit board 11 by inserting leads of these circuit components into the printed circuit board 11. The leads of the components 12 and 13 are soldered on a soldering surface of the printed circuit board 11 so that solder lands 12a and 13a are formed on the soldering surface.
The aforementioned safety standards requires that the distances between the high-voltage component 12 and the low-voltage component 13 are as long as an appropriate insulation space distance defined by the safety standards. In the case shown in FIG. 1A, the distances between the components 12 and 13 includes a distance X and a distance Y. The distance X is the shortest distance between the components 12 and 13 on the mounting surface side, and the distance Y is the shorted end-to-end distance between the components 12 and 13 on the soldering surface side. The insulation space distance is the distance X or Y which is shorter than the other under a condition where there is no parts between the components of concern.
The appropriate insulation space distance is an insulation space distance depending on the potential difference between the components 12 and 13. For example, if the potential difference is equal to 100 V, the appropriate insulation space distance between the components 12 and 13 is equal to or longer than 4 mm. Hence, when the high-voltage component 12 and the low-voltage component 13 are mounted on the same printed circuit board 11, the components 12 and 13 are spaced away from each other by the appropriate insulation space distance defined by the safety standards.
Japanese Laid-Open Patent Application No. 57-211714 discloses an insulation spacer designed taking into account the above insulation space distance. FIG. 1B shows a spacer 14 proposed by the above Japanese Application. The spacer 14 is interposed between the high-voltage component 12 and the low-voltage component 13 and is in contact with the facing sides of these components. The insulation spacer 14 has an approximately T-shaped cross section and is made of an electric insulation material. The insulating spacer 14 has a head portion, which ensures the distance X between the high-voltage component 12 and the low-voltage component 13. When the insulation space distance between the high-voltage component 12 and the low-voltage component 13 is X dependent on the potential difference therebetween, the insulation spacer 14 ensures the distance X and prevents a reduction in the distance X due to an inclination of the component 12 or 13 or both.
However, even in a case where the high-voltage component 12 and the low-voltage component 13 are disposed in areas close to each other on the mounting surface of the printed circuit board 11, these components must be spaced apart from each other by the appropriate insulation space distance depending on the potential difference between the components 12 and 13 irrespective of whether or not the insulation spacer 14 is used. Hence, it is very difficult to facilitate down-sizing of the printed circuit board 11 and thus the electric products using the board 11. Further, as the potential difference between the components 12 and 13 becomes greater, the insulation space distance becomes longer. This also prevents down-sizing of the printed circuit board 11.